Fix a bug in a formula.

git-svn-id: https://svn.dealii.org/trunk@19312 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/doc/news/changes.h b/deal.II/doc/news/changes.h
index e9e97e08a0fd59cdd550a22ac21ea56002bdb545..876a9c5cf4b62fb0618a3169920166a61ae9ec3b 100644 (file)
--- a/deal.II/doc/news/changes.h
+++ b/deal.II/doc/news/changes.h
@@ -82,6 +82,26 @@ inconvenience this causes.
 <h3>General</h3>
 
 <ol>
+   <li>
+   <p>
+   Fixed: @ref step_31 "step-31" had a bug in the computation of the
+   global scaling parameter in the function that evaluates the artificial
+   viscosity: we computed
+   $c(\mathbf{u},T) = 
+    c_R\ \|\mathbf{u}\|_{L^\infty(\Omega)} \ \mathrm{var}(T)
+    \frac{1}{|\mathrm{diam}(\Omega)|^{\alpha-2}}$
+   when it should have been
+   $c(\mathbf{u},T) = 
+    c_R\ \|\mathbf{u}\|_{L^\infty(\Omega)} \ \mathrm{var}(T)
+    \ |\mathrm{diam}(\Omega)|^{\alpha-2}$. This didn't matter much in this
+   program because $\mathrm{diam}(\Omega)=2^{1/\textrm{dim}}$ and so is close
+   to one. It would matter, however, if the domain had been different, as
+   it is, for example, in @ref step_32 "step-32".
+   <br>
+   (WB 2009/08/19)
+   </p>
+   </li>
+
    <li>
    <p>
    Changed: When using Trilinos wrapper objects in parallel through MPI, each

diff --git a/deal.II/examples/step-31/step-31.cc b/deal.II/examples/step-31/step-31.cc
index e33facb240e632bef16a461fbeef1f6e1b5be32f..6125b21223ab35046948f9b0a72e3f6d0aea5748 100644 (file)
--- a/deal.II/examples/step-31/step-31.cc
+++ b/deal.II/examples/step-31/step-31.cc
@@ -1023,7 +1023,7 @@ compute_viscosity (const std::vector<double>          &old_temperature,
       max_velocity = std::max (std::sqrt (u*u), max_velocity);
     }
   
-  const double global_scaling = global_u_infty * global_T_variation /
+  const double global_scaling = global_u_infty * global_T_variation *
                                std::pow(global_Omega_diameter, alpha - 2.);
 
   return (beta *